The invention relates to a method of and to an apparatus for applying one or more layers of coating material (such as an adhesive) to a running web of paper (such as crepe paper), textile material, plastic material or the like. More particularly, the invention relates to improvements in methods of and apparatus for applying to a running web a coating material which contains a solvent, particularly a solvent which warrants or necessitates recovery.
It is already known to convey a web which carries a layer of coating material through a chamber which is sealed from the atmosphere and wherein the coating material is heated to promote the release of solvent so that the latter can be evacuated from the chamber. The chamber is normally filled with an inert gas (i.e., a gas other than air or oxygen), and it is normally necessary to recover the solvent from the inert gas. Such procedure is often resorted to in connection with the making of webs or strips which are coated with a pressure-sensitive or other adhesive, e.g., in connection with the making of adhesive-coated transparent or translucent tape. The inert gas is or can be nitrogen (N.sub.2). The purpose of the exclusion of air or oxygen is to render it possible to operate with a high percentage of solvent per unit of volume without the danger of explosion.
A drawback of conventional apparatus which are used to apply solvent-containing coating materials directly to a running web or tape is that losses in inert gaseous fluid are very high unless the chamber is sealed from the atmosphere in a manner which contributes excessively to the cost of the apparatus and of the ultimate product. Inert gases fluid is most likely to escape in regions where the web or tape is introduced into and where the coated web or tape is evacuated from the drying zone of the chamber. As a rule, the application of solvent-containing coating material takes place in a separate zone of the chamber and the thus coated increments of the web are thereupon introduced into the drying zone. The cost of sealing means (especially contact-free sealing means) in the regions where the web or tape enters into and leaves the drying zone of the chamber is very high, especially since it is necessary to separate from the incoming web or tape the (boundary) layer of atmospheric air (either directly from the tape or from the freshly applied solvent-containing layer of coating material) as well as to prevent penetration of atmospheric air into (and hence the escape of inert gaseous fluid from) the drying zone.
Another drawback of conventional coating apparatus is that breaks of the web in the interior of the chamber necessitate an opening of the chamber with attendant huge losses in inert gaseous fluid and prolonged interruptions of the coating operation. As a rule, each opening of the chamber must be preceded by complete evacuation of inert gaseous fluid which entails a lengthy interruption of the coating operation and the aforementioned huge losses in nitrogen or other inert gaseous fluid.